Event Recorders at Protection Systems
Mustafa İŞBECEREN1
Nevzat ONAT2
1Telepro Energy and Electronic Systems San. Trade Ltd. Sti., 34785, Atasehir, Istanbul
2Marmara University, Vocational School of Technical Sciences, 34722, Kadıköy, Istanbul
Summary
In this study, the reasons for recording the events occurring in the protection systems, the types of event and event/fault recording systems were investigated. Event recording equipment has a very important function in improving the parameters that directly affect the power quality of the system, such as reliability and stability. With the correct analysis of the instant and statistical data they provide, downtime in energy systems can be shortened. By determining the error sources as a result of statistical analysis; Necessary maintenance, repair, replacement decisions can be made in advance, and possible interruptions can be prevented or cleaning times can be shortened by preventing the spread of the malfunction.
Introduction
Power quality in energy systems is a concept that encompasses the detection and analysis of a wide variety of fault events, which in some cases lead to the shutdown of very important production processes and cause great financial losses. This concept is basically based on reliability analysis, which examines the probability of failure of each element in the system and the de-energization of consumers. The term reliability is based on the assumption that the installed power and energy supply in the system feeds all consumers. Although interruptions or losses that may occur due to insufficient installed power directly affect this concept, they are not included in its definition. There are models based on many probability calculations to predict failure rates of an element. These include studies of the time-varying Weibull distribution of element failure states and uptime. However, there may be some discrepancy between generally predicted failure rates and encountered failure rates due to the following factors:
- Description of the fault,
- Comparison of the predicted environment with the real environment,
- Test equipment, sustainability, support and dedicated staff,
- The element failure rates and the actual failures of the elements, which are accepted while forecasting,
- Manufacturing methods including inspection and quality control,
- Distribution of failure times,
- Independence of element failures [1].
Reliability analysis of a distribution system is generally concerned with its performance at the consumer end of the system, ie at the load points. The main indexes used to predict the reliability of a distribution system are:
⦁ Load point failure rate,
⦁ Average downtime and annual unavailability.
Base indexes are important to an individual consumer point, but they are not sufficient to make a comprehensive system performance evaluation. An additional set of indexes can be calculated using these three base indexes and the number of load/consumers connected to each load point within the system. Most of these additional indexes are weighted averages of baseload point data. The most common additional directories or system directories:
⦁ System Average Interruption Frequency Index (SAIFI),
⦁ System Average Interruption Duration Index (SAIDI),
⦁ Customer Average Interruption Duration Index (CAIDI),
⦁ Average Service Availability Index (ASAI),
⦁ Avarage Service Unavailability Index (ASUI),
⦁ Energy Not Supplied (ENS),
⦁ Avarage Energy Not Supplied (AENS).
These system indexes can also be calculated by making extensive use of system outage data and providing valuable data on the historical performance of the system. It is extremely important to use past performance metrics to be able to calculate the same base indexes for the future performance of the system. The reliability indexes of a distribution system are purely random functions of failures, times of repairs and replacements. Therefore, the calculated indexes are random variables and can be expressed by probability distributions. Traditional distribution system reliability assessments normally only deal with the mean values of the calculated indexes. Further noteworthy additional information is the relationship of each calculated sequence to the planners, designers, and managers of the distribution system. According to the report of the IEEE (Instutie of Electrical and Electronics Engineering) committee, an equipment failure report should contain the following basic information:
⦁ Type, design, manufacturer and other information necessary for classification,
⦁ Installation date, location of the system, length if there is a line,
⦁ Type of fault (short circuit, incorrect operation, etc.),
⦁ Cause of malfunction (lightning, tree, etc.),
⦁ Time of failure (time out of service and return to service rather than downtime only), date, and meteorological conditions.
⦁ Outage type (forced or planned, temporary or permanent).
In addition, the committee recommended that the total number of similar personnel in service be included in the report in order to obtain the rate of failure of each employee in each service year. It also recommends reporting every element failure without discrimination, whether it interrupts the service or not, in order to find the failure rate of the element correctly. Failure reports provide invaluable information for component replacements and preventive maintenance programs [2, 3].
Disable Definitions in Energy Systems
Reliability analysis also requires knowledge of the types of outages. Most of the definitions below are terms used to analyze and report electrical distribution unit outages and shutdowns, and are accepted by the US Institute of Electrical and Electronics Engineers:
⦁ Outage: An element is defined as a situation in which it cannot perform its normal functions due to some events directly related to that element. A downtime event may or may not cause an interruption in the service provided to consumers, depending on the system structure.
⦁ Forced Outage: It is a failure that occurs in hazardous situations that are directly related to an element and require the element to be taken out of service immediately. It can be achieved either automatically or by switching operations as fast as possible. Another variant is unnecessary downtime as a result of equipment or human error.
⦁ Scheduled Outage: A failure where an element is deliberately taken out of service at a specified time, usually for structural, preventive maintenance, or repair purposes. It is understood as follows whether a shutdown is forced or planned. If an addition is requested, the deactivation event can be delayed. This type of deactivation is planned. Otherwise it is forced disablement. A shutdown delay may be required, for example, to prevent overloading of facilities or interruption of service to consumers.
⦁ Partial Outage: It is the situation where the capacity of an element to perform its function is reduced but not completely destroyed.
⦁ Transient Forced Outage: It is the situation where, when the condition causing the failure of a disabled element is removed immediately, the affected element can be automatically brought back into service by a quick switching or reclosure of the breaker or by changing a fuse. An example of a temporary forced failure would be a lightning flash in which the element exposed to the lightning does not remain on all the time.
⦁ Persistent Forced Outage: Failures, the cause of which is immediately repaired, but before commissioning, the affected element must be corrected by replacement, repair, or elimination of the hazard. An example of this type of event is a lightning flash that ruptures an insulator, thereby blocking the circuit until the element is repaired or replaced.
⦁ Interruption: It is the loss of service of one or more consumers or other units as a result of the failure of one or more elements depending on the demand structure.
⦁ Forced Interruption: It is an interruption caused by a forced outage.
⦁ Scheduled Interruption: An outage caused by a planned outage.
⦁ Momentary Interruption: This outage has a limited time period required before it can be serviced again by automatic or remote control operations or manual switching at any operator’s location. Switching operations are usually completed within a few minutes.
⦁ Temporary Interruption: This interruption is manually switched, where an operator is not present at any time, a switching period must elapse before the service can be restored. This type of switching operations is completed in 1-2 hours.
⦁ Sustained Interruption: It is an interruption that cannot be classified as momentary or temporary [2, 3].
The faults that cause the interruptions, the definitions of which are given above, are grouped into four main groups:
⦁ Transient Failures: These are faults of very short duration and typically cleared very quickly by breaker operation. These events are usually cleared before 8 periods in high speed protection systems and before 16 periods in selective systems.
⦁ Short-Term Failures: All other time-delayed protection and re-activation events, which generally have no effect on the operation (stability) of the system, are covered by this concept. These event durations are in the range of 20-60 periods. If more than one protection action is required to clear the fault, they may take longer. Bu olaylar genellikle doğru koruma işlemlerini, arıza yerini veya sistem model parametrelerini doğrulamak için analiz edilirler.
⦁ Long-Term Failures: Such events are faults that affect system stability, such as power oscillations, frequency variations, and abnormal voltage problems. They are often analyzed to identify causes of faulty system operations. Data management techniques are used to process large numbers of samples and ensure the required parameters are recorded.
⦁ Steady-State Failures: These are continuous disruptive effects that do not threaten the operation of the system but affect the power quality. These types of faults may include interactions between components of the power system and/or harmonics produced by loads. Depending on the type of fault, recording systems with high sampling numbers should be used to detect the necessary data and events [4].
Event Recorders
As can be seen from the fault definitions above, recording and analysis of faults occurring in energy systems is a very important process and detailed records containing as many parameters as possible should be kept. This process has been applied in various ways with the use of protection systems in power systems. For many years it was done by means of ready-made forms, fault logs and recording the event on personal computers by operators. The fact that this method has very important drawbacks and is insufficient to provide the statistical data required for the above-mentioned reliability analysis makes it necessary to perform the event recording process independently of individuals. Figure 1 shows the types of equipment and systems for event recording. Sequential event recorders within the scope of this study are devices that record every state change in the system without time delay.
Today, digital fault recorders and microprocessor-based protection relays, which have been used for many years, can record faults in various forms and directories. However, in the fault records made with this system, there are significant difficulties and confusions in the data storage of each device in different formats, the collection and analysis of the data held by more than one device in a center. In addition, in some events, the data received may be inaccurate due to the time synchronization between these devices by more than one device recording the same event. The use of event recording systems, which can eliminate these drawbacks and record faults occurring in very large network parts in a single center without time delay and share them in various ways with software-controlled authorization, is becoming widespread. Event recording; It is carried out for two main purposes as recording all the movements in the system that are not faults or malfunctions and monitoring the performance of the protection system. The advantages of these systems over microprocessor-based event recording relays or digital fault recorders can be summarized as follows:
⦁ They are independent of faults or partial save errors that occur in the relays,
⦁ Many digital relays filter out analog signals and do not take them into account in fault records. Event recorders record all signals,
⦁ They have higher recording memory and can keep long-term recordings,
⦁ They have faster sampling rates,
⦁ Frequency responses are wider,
⦁ They are designed to include more trigger options,
⦁ They can monitor many power system components simultaneously,
⦁ It can be used to monitor the factors affecting power quality especially in wind and solar, flexible AC transmission systems, static VAR generators, arc furnaces and variable frequency drive systems,
⦁ They can provide useful information in monitoring the high initial switching currents of large power auto transformers used in parallel operation combinations and analyzing the problems they may cause,
⦁ They can present system responses in a wide spectrum during faults,
⦁ Analysis of detailed and single-center fault records is facilitated,
⦁ Errors and delays caused by the operator can be detected,
⦁ The propagation directions of the faults can be detected quickly and it becomes possible to take the necessary precautions. Thus, possible power outages or equipment damage can be prevented/reduced,
⦁ As a result of statistical analysis, operator errors, causes of delays, concentration points of failures, seasons and many additional information can be obtained for many centers. Thus, the system performance can be improved by planning the necessary maintenance, repair and replacement activities [5].
Fault events create transient regimes in a very short time until the protection system is activated. Therefore, the most important parameter in event recorders is the sampling number of the system. The more data is received during the event, the more healthy the developmental stages of the event can be followed. The accuracy of these data has a direct impact on the results of the technical and statistical analyzes to be made later. Figure 2 shows the effect of sampling time on signal quality for a one-period sine wave [6].
The main purposes of event recording systems on a large scale can be briefly explained as follows:
⦁ They help in a good resolution of events that occur in the field in networks and are directly related to power quality,
⦁ They assist in the development of appropriate software and hardware tools to help identify, prevent and/or mitigate potential problems if they occur,
⦁ They help to provide optimal usage possibilities that coincide with the purpose of preference of multi-functional smart electronic relays, enabling them to fully fulfill their protection, control and monitoring functions in distribution stations or industrial environments,
⦁ They undertake the task of providing communication hardware that allows simultaneous access over multiple serial or local network interfaces and supports standard industrial protocols,
⦁ They contribute to reducing installation and maintenance costs.
An example of an event recording system is presented in Figure 3. Events detected by field gauges and relays are first collected in the input module. This unit provides significant technical and economic advantages by ensuring that all inputs are gathered in a single point and that the communication after this point is made only with communication cables. The input module sends some data to alarm transmitters under software control. At the same time, it sends all event data to the remote access unit (RTU) and allows it to be saved in the memory area of this device. The RTU device performs the function of simultaneously transmitting the fault information to the operator’s computer in the center where the event occurred and to other desired output units. With the time clock and meteorology station units that generate the signal with the GPS-based IRIG-B code operated within the RTU device, the data related to the time and climate conditions described above and which should be in a fault record are also recorded together with the fault. The process of transferring this information to the internet via MODEM, sending it to various units in remote centers without delay, and recording it in the database in the main service provider system in the energy management unit can be easily performed. In this system, the communication protocol and software used are as important as the hardware. The fact that these software have analysis capabilities and user-friendly interfaces suitable for the desired purpose significantly increases the performance of the system. It is also provided by software authorization, at what level and by whom the data sent to the server system can be seen.
Result
Event recording systems provide significant advantages over other options in the creation of statistical databases, especially by recording all events sequentially and without time delay. As for the installation cost, for example, compared to a digital relay, they require additional equipment such as RTU, Input Module, Server. However, they provide very important technical and economic benefits with their direct and indirect contributions to the improvement of stability and reliability indices that directly determine the concept of power quality in energy systems. It can be said that event recorders will have a very wide usage area in the near future compared to other recording systems due to their long-term, uninterrupted recording capability, software authorized access flexibility, and superiority in reporting and recording analysis.
Sources
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[3] Gönen, T., Electric Power Distribution System Engineering, University of Missouriat Columbia, pp. 577-98, July, 1985.
[4] W. Strang, J. Pond, Considerations for Use of Disturbance Recorders, A report to the System Protection Subcommittee of the Power System Relaying Committee of the IEEE Power Engineering Society, pp.4-5, USA, 2006.
[5] J. Perez, “A Guıde to Dıgıtal Fault Recordıng Event Analysis”, 63rd Annual Conference for Protective Relay Engineers, pp.1 – 17, Canada, 2010.
[6] H. Davila, “Records from DFRs vs. Records from Microprocessor-Based Relays”, Transmission and Distribution Conference and Exposition: Latin America (T&D-LA), pp. 635-644, 2010.
[7] www.telepro.com.tr